Means for producing time lag in electrical circuits



Jan. 19, 1937. L. M. IL GENFRHTZ MEANS FOR PRODUCING TIME LAG IN ELECTRICAL CIRCUITS Original Filed Sept. 14, 1926' ATTORN EY Pumas] .1.11. d 19, 1931 UNITED STATES PATENT osi-lcs MEANS FOR PBODUCING TIME LAG 1N ELECTRICAL CIRCUITS Original application September 14, 1926, Serial 135,447.- Divided and this application March 19, 1930, Serial No. 437,209

- 4 claims.

This invention relates to a method and means .for producing a time lag in the operation of a. device connected with an electrical circuit, and particularly to means for preventing the undesired operation of a current responsive device such as an alarm signal connected with the pilot channel apparatus of a carrier signaling system.

This applicationis a division of my copendingapplication, Serial No. 135,447, led September 14, 1926, and is intended to particularly cover a pilot channel alarm system having a delay circuit to prevent operation by transient disturbances.

In carrier signaling systems, it is customary to transmit,4 simultaneously with the channels representing the telephone or telegraph signals, a separate channel known as a pilot channel consisting preferably of a single frequency of constant amplitude. At the various repeater stations along the linel and also at the receiving terminal, this pilot channel is filtered out, and its variations from normal indicate the changes in the transmission equivalent of the system resulting from variations in the constants of the line, and serve to determine the changes necessary in repeater amplification to restore the transmission equivalent to normal. At the repeater stations, it .has been customary to use the pilot channel to operate an alarm whenever the pilot current in the loutput side of theamplifier at that station varied from normal by a predetermined amount. It has been found that a false alarm signal may sometimes be produced as an indirect result of the speech or other signaling channels that are being amplied, together with the pilot channel at the station at which the alarm is produced. For example, the heavy side band loads of the signaling channels sometimes overload the repeater so as to cause variations in the pilot channel current at the repeaters and the receiving station, which variations momentarily exceed xed limits. Those side bands may be located in the frequency spectrum close to the side bands representing the signaling channels, e. g. between a side band and the carrier upon which the side band is predicated. Unless the alarm' circuits are protected against such transient variations of the pilot channel, false indications will be given by the alarm circuit. Obviously, the pilot channel selective network may be designed vto prevent a momentary surge of speech or lsignal frequency `current from affecting the alarm'directly, but it is not economical to go to the ultimate extreme to effect such result, and furthermore,

(ci. 117-311) A this selectivity does not prevent interference from overload. Therefore, since a certain amount of interference from the speech or higher frequency signaling channels must be tolerated, an alarm circuit is required that is not subject to abnormal currents of short duration, and still will operate reliably upon an abnormal current that persists a predetermined length of time.

It is the object of this invention to provide circuit, whereby the alarm or other current responsive device will not operate upon transient currents, but will operate upon currents continuously applied for a predetermined length of time.

Other objects of this invention will be apparent from the following description when read in connection with the attached drawing, of which Figure 1 shows schematically a simple form of embodiment of the invention, and Fig. 1a is a graph illustrating the principle involved in the invention.

In Fig. l, the line L1 represents a signaling circuit over which a plurality of carrier channels may be transmitted from station A to station B, and vice versa. interposed at various points between the terminals of the line are a plurality of repeaters designated R1, R1", R2, Rz and Ra and R3. The repeaters R1, Rz, and R3 serve to amplify the channels transmitting in one direction, and the repeaters designated by the same symbols primed operate upon the channels in the opposite direction. Connected with the output of the repeater R1 is an alarm circuit which is connected with the line L1 through the lter F1 and the amplifier A1. The filter is of a type designed to pass the pilot channel frequency which, when amplified, will be impressed upon the rectifier D1. The grid circuit of this rectiercontains the circuit i which is tuned to the pilot channel frequency. The plate circuit includes a marginal relay -2 which is designed to operate whenever the change in plate current'exceeds a predetermined value, which value will be dependent upon the magnitude of the voltage impressed upon the grid of the rectifier D1. It is desirable to make clear that while a vacuum tube rectifier has been shown, any Well-known form of device to convert the alternating current of the pilot channel to a direct current may be employed.

Connected with the armature and the contacts of relay 2 is an auxiliary relay 3, the said connec-V tion including a source of potential 4, a resistance 5 and a condenser 6, the latter elements serving as a spark killer for the contacts of relay 2. The

1o I means for introducing a time lag in an alarm closing oi'reither contact of the marginal relay 2 will close the circuit of the auxiliary relay 3, which is preferably slow-acting in order to avoid trouble arising from the jarring of the relay. Whenever relay 3 is energized, the circuit controlled by its armature will be open. When it is deenergized and the circuit is closed, the source of potential 1 will be connected across the terminals of the condenser which is of normally large capacity. This connection, however, is shunted by the resistance 9 of fairly large magnitude which provides apath through which the condenser may discharge whenever the contact of relay 3 is open. The grid and lament terminals oi the rectifier Dz are connected across the source 1, the resistance 9 and the condenser B in such manner as to reduce the plate current of the tube either to zero or to a negligibly small value. The plate circuit of the rectier Dz includes a source oi current I0 and a relay Il. which relay controls an alarm I2 which may be a buzzer or other suitable device. Connected in. parallel with the battery I0 and the winding of relay II is a circuit including a resistance I3, a key i4 and a contact of relay Il. The contact of key I4 is normally closed. Consequently, when relay Il operates and closes both its upper and lower contacts, it will cause the alarm I2 to operate, and will also lock itself over a circuit which includes the source i0, the winding of relay II, resistance I3, upper contact of relay Il, and the normally closed contact of key I4. The purpose oi this locking circuit is -to cause the alarm to operate continuously once it has begun to operate, thereby ensuring that the repeater attendant will respond to the alarm and take such action as is necessary to vadjust the repeater circuit. The opening of the key I4 restores the alarm to its normal condition.

The `manner in which the alarm circuit operates in order to introduce the necessary time lag to avoid false operation is as follows: Let it be assumed that signaling channels and a pilot channel of normal magnitudes are operating between station A and station B through the repeater R1 and the repeaters at subsequent points operating in the same direction as R1. The normal pilot channel voltage impressed upon the lter Fi would be transmitted therethrough and amplified by A1. This voltage would then be impressed upon the rectifier Di. This grid voltage, which results-from the normal pilot voltage, causes a current of predetermined magnitude to ow through the plate circuit of the tube. This current flowing through the winding of the marginal relay 2 would tend to cause the armature thereof to move in a certain direction, but such movement would be prevented by a biasing spring, the tension upon which would be just.suiiicient to neutralize the magnetic pull due to the normal plate current so that the armature oi relay 2 remains at a point midway between its contacts. When this condition exists, the circuit including relay 3 is open, so that its armature is not attracted. Accordingly, the voltage of the source 1 will be applied to the condenser 8 and serves to charge the condenser to the full voltage of the source. This voltage will also be impressed upon the grid of the rectifier D2 inasmuch as the resistance 9 is of very large value. The negative voltage of the magnitude E, shown in Fig. la, is more than sufficient to reduce the plate current of the rectifier D2 to zero. Consequently, relay Il will not be energized and the circuit of the alarm device will not be closed. Relay II is adjusted to operate at the plate current that results from the negative grid voltage e, shown in Fig. 1a. From this figure, that represents the relation between voltage across the condenser and time, it will be seen that after the opening of the contact oi relay 3 an appreciable amount oi' time elapses before the voltage of the condenser il drops from E1 to e. It is by virtue oi this fact that the operation of the alarm l2 may be delayed until the voltage of a magnitude necessary to set in operation the alarm circuit has continued a predetermined length oi time.

The manner in which the time-lag arrangement operates is as follows: Let it be assumed that by overloading of the amplifiers, or for some other reason, the voltage of the pilot channel rises above normal to the extent that is considered undesirable. When such` voltage is applied to the grid of the rectifier D1, the plate current of that tube will cause the marginal relay to move its armature to one of its contacts, which will close the circuit of relay 3 and in turn will open the circuit between the source 1 and the condenser 8. The disconnection of the source oi. charging voltage will cause the condenser 8 to discharge, and the rate of discharge depends upon the resistance 9, size of condenser, and the voltage ratio The elements are so proportioned that the time elapsing between the opening of the contact of relay 3 and the instant when the voltage acro the condenser 8 reaches the value e is greater than the longest interval in which speech currents owing through the amplier Ri would exceed the normal level. That is to say, ii the abnormal variation of the pilot channel voltage is due to the overloading of an amplifier by the speech or the carrier signal channels, the discharge rate of the condenser may be so controlled that the overloading of the amplifiers will cease before the condenser voltage drops to e. The relay II and the alarm device I2 will not operate because, as stated above, it required a plate current corresponding to the grid voltage e to operate relay II. It will be seen that the alarm was not produced even though the pilot channel voltage exceeded normal to such extent as to operate the marginal relay 2.

If, on the other hand, the nature of the trouble is such as to cause the abnormal pilot channel voltage to persist for a length of time greater than that represented by T, the grid voltage of Dz will fall below e and the plate current will rise to a value sufficient to operate relay I I. This will operate the device I2 which continues to give an alarm signal until the attendant responds and opens the locking circuit of relay I I by presslng the key I4.

In like manner, if the level of the pilot channel voltage dropped to or below the predetermined lower limit, the plate current through the relay 2 would be diminished and the armature i would be drawn to its other contact by the tension of the spring. This operates relay 3 and causes the operation of the alarm I2 in the same manner in which an over-voltage effected such operation.

The invention resides broadly in a method and means for preventing the operation of a current responsive device unless and until the primary operating force has persisted a predetermined length of time. In the circuit arrangement chosaoeaaos en to describe the invention the current responsive device has been styled an alarm signal. It is, of course, obvious that the current responsive device, by which is meant the element whose time of operation is controlled, may take any one of a number of different forms. For example, it may be an automatic control device, the function of which ls to automatically adjust the repeater so as to control its gain, and thus keep constant the overall equivalentl of the system.

While I have described this inventionin connection with the control of a current responsive device-upon pilot channel circuits of carrier signaling systems, it is, of course, obvious that the invention is not limited to this particular use, but may be applied in other iields where it is desirable to introduce a time lag in an electrical circuit in order to prevent the operation of a device until the cause of such operation has persisted a predetermined length of time.

Furthermore, while the invention has been disclosed as embodied in a particular form and arrangement oi' parts, it is capable of embodiment in other forms and arrangements without departing from the spirit and scope of the appended claims. i

What is claimed is:

l. In a system to delay the operation of a device until the operating voltage has persisted a predetermined length of time, the combination with a source of potential the variations of which from normal are to be indicated, of a marginal relay having an armature the position of which for normal currents is midway between its contacts, an auxiliary relay having its winding effectively connected to a source of current and to the contacts of the marginal relay so as to be energized upon the closing of either contact, a condenser, a source of voltage, a vacuum tube having its input connected with the said condenser and the negative pole of the said source oi voltage through the armature and contact of the said auxiliary relay, and an alarm circuit connected with the output of the said vacuum tube.

2. In an arrangement for controlling the time of operation of an electro-responsive device, the combination with a source of alternating voltage, of an alarm device, the operation of which depends upon the predetermined duration of the voltage of the said source at a predetermined level above or below normal, means to rectify said alternating voltage, switching means responsive to the said 4rectiiying means operable Whenever the rectiiied currents depart to a predetermined extent from normal, an energy storage circuit including a condenser, a source of direct current to charge the said condenser and a high resistance to control the rate of discharge thereof, a vacuum tube having its input circuit connected across said energy storage circuit and its output circuit connected with the said alarm device and means controlled by the said switching means to effectively disconnect kthe said source of direct current fromthe said condenser whenever the rectified alternating current departs from normal to a predetermined extent.

3. In a system to delay the operation of a device until an operating voltage of a predetermined magnitude has persisted a predetermined length of time, the combination with a source of potential the variations of which from normal are to be indicated, o! a relay responsive to said variations of potential, an auxiliary relay adapted to be energized by the operation of said rstmentioned relay, a vacuum tube amplifier having connected between the illament and grid thereofl a source of negative biasing voltage shunted by a condenser and also by a resistance, a third relay connected to the plate circuit of said tube and an alarm controlled thereby, the said auxiliary relay being arranged to effectively disconnect the said source of negative biasing voltage from said grid whenever the potential variations of said source exceed prexed limits.

4. In a carrier signaling system in which a pilot channel is employed to determine variations in the transmission conditions existing in such system, the combination with a line over which the carrier channels are operated, of means connected to said line to select the pilot channel frequency, means to amplify and to rectify the selected frequency, a vacuum tube amplier having a signaling device connected to the plate circuit thereof, an input circuit connected to the grid of the vacuum tube, and including a negative biasing source shunted by a condenser and also a resistance, means responsive to the rectiiled pilot channel voltage to eiectively disconnect the said biasing source from said input circuit when the variations of the pilot channel voltage exceeds preiixed limits.

LESTER M. ILGENFRITZ. 

